Subsurface pump



M. L. HART Jan. 7, 1969 SUBSURFACE PUMP Sheet Filed Jan. 13, 1967zzvvmvron. Mae/0,4 La H/wr M. L. HART SUBSURFACE PUMP Jan. 7, 1969 FiledJan. 13. 1967 TLEE fizz-[i INVENTOR. A. HA/er ME- /bA M. L. HARTSUBSURFACE PUMP Jan. 7, 1969 Filed Jan. 13, 1967 r1511 fits-i2 INVENTOR.L. HA r United States Patent 6 Claims ABSTRACT OF THE DISCLOSURE Ahydraulically operated, rodless pump for use in subsurface pumping. Thepump includes concentric power fluid and production fluid strings, andhas a free, compound working piston mounted in the power fluid stringand driven'downwardly therein by a hydraulic power fluid delivered fromthe surface. The upward stroke of the compound working piston isassisted by the hydrostatic head exerted by production fluid standing inthe annulus between the strings, and by pneumatic pressure exerted by agas entrapped above production fluid collected in a production fluidcollection chamber at the top of the production tubing. Means isprovided for automatically and continuously maintaining a constantvolume of power fluid in the column of power fluid which extends betweena power fluid piston located at the surface and the compound workingpiston located down hole.

This invention relates to a subsurface pump of the type used to produceliquids from a subterranean deposit. More specifically, but not by wayof limitation, the present invention relates to a subsurface pump whichconcurrently uses hydraulic, hydrostatic, and pneumatic forces forefliciently producing petroleum from an underground formation.

Subsurface pumps utilizing a liquid piston in place of a metallic suckerrod string, and employing balanced columns of liquid to assist in thelifting of liquid from great depths and to reduce the power requirementsof the pump have been heretofore proposed. This has been prompted by therecognition for some time, that due to the great depths to which wellsfor producing petroleum are now being drilled, the traditional suckerrod type pump is no longer satisfactory for producingoil from deep wellsof this type. The rodless, subsurface pump system has the advantage ofeliminating the long and heavy sucker rod string utilized in the olderpumps, thus reducing the overall expense of pumping, and improvingmaintenance costs.

The present invention provides an improved, hydraulically driven'subsurface pump which provides assistance to the main-hydraulic powersource in the form of a leg or column of liquid exerting hydrostaticpressure in a balancing action during an appropriate and pre-selectedtime during the pumping action, and also providing pneumatic assistanceto reduce the total power required for pumping. The pump of the presentinvention is an improvement over subsurface, hydraulically operatedpumps in several other respects. Thus, means are provided forautomatically maintaining substantially constant the length of the powerfluid rod which extends from a piston at the surface to a working pistonwhich is located deep in the well so that losses of power fluid throughleakage, and also thermal expansion of the power fluid, can beautomatically compensated. The pump also provides means for removing asubstantial part of the gas produced with the oil, as well as otherfeatures which assist in reducing or eliminating gas lock. Finally, thepump includes an improved sand trap feature which reduces the sand andsediment content of the produced oil, and facilitates easier and moreconvenient cleaning of the sand trap.

Broadly described, the subsurface pump of the inven- 3,420,183 PatentedJan. 7, 1969 tion comprises a power fluid tubing string and a productionfluid tubing string which concentrically surrounds the power fluidtubing string and defines an annulus therewith. A free working piston isreciprocally and slidingly disposed in the power fluid tubing string,and a first check valve is disposed in the power fluid tubing stringbelow the free piston for permitting flow of fluid upwardly in the powerfluid tubing string while preventing the flow of fluid downwardly pastthe check valve. Passageway means extends through the power fluid tubingstring at a location between the first check valve and the free piston,and places the annulus between the power fluid tubing string and theproduction fluid tubing string in communication with the interior of thepower fluid tubing string. A second check valve is disposed in saidpasageway means for preventing flow of production fluid from saidannulus into said power fluid tubing string through the passagewaymeans.

The free piston includes an upper piston element and a lower pistonelement with the upper and lower piston elements being interconnected byan elongated connecting rod. A second passageway means is formed throughthe power fluid tubing string to place the annulus between the two tubesin communication with the interior of the power fluid tubing string,such second passageway being formed at a point in the power fluid tubingstring that is located between the upper and lower piston elementsduring the reciprocation of the free piston in the power fluid tubingstring. The second passageway means permits a column of productionliquid standing in the annulus between the production fluid tubingstring and the power fluid tubing string to substantially balance oroffset the weight of the power fluid above the piston in thepower fluidtubing string so that a minimum power requirement is involved in liftingthis piston and the column of power fluid upwardly during the upstrokeof the subsurface pump.

Secured to the upper end of the power fluid tubing string is a powerfluid cylinder in which is mounted a reciprocating power fluid piston.Any suitable driving means is provided for driving the power fluidpiston in reciprocation in the power fluid cylinder for directing thepower fluid down into the power fluid tubing string during the downstroke of the free working piston in this tubing string. Means areprovided adjacent to the power fluid cylinder for supplying makeup powerfluid to this cylinder, and the power fluid piston mounted in the powerfluid cylinder is equipped with suitable valving so that a substantiallyconstant volume of power fluid can be maintained in the column of powerfluid which extends between the power fluid piston and the free workingpiston disposed in the lower portion of the power fluid tubing string ashereinbefore described.

A preferred embodiment of the pump also includes in addition to thedescribed structure, a production fluid collection chamber which isdisposed at the surface and is connected to the upper end of theproduction tubing string to receive production fluid therefrom. Theproduction fluid collecting chamber has connected thereto a dischargeline in which is interposed a balanced hydrostatic fluid level controlvalve which is responsive to the accumulation of a predetermined amountof production fluid in the production fluid collection chamber to permitthis fluid to be periodically discharged through the discharge line. Agas supply system is connected to the upper portion of the productionfluid collection chamber and functions to supply a gas under pressure tothe collection chamber for pneumatically assisting the discharge ofproduction fluid from this collection chamber, as well as to assist thehydrostatic balancing effect of the column of production fluid as itacts in opposition to, or balances, the

column of power fluid extending above the free working piston in thepower fluid tubing string.

From the foregoing description of the invention, it will have becomeapparent that it is an important object of the present invention toprovide an improved subsurface pump which employs hydraulic, hydrostaticand pneumatic forces to more efficiently produce subterranean liquidswith a power input requirement which is lower than has beencharacteristic of the subsurface pump systems heretofore utilized.

Another object of the invention is to provide a subsurface pump which,in operation, displaces substantially 100 per cent of the effective borecapacity of the pump barrels with power fluid and production fluid oneach stroke of the pump, thereby substantially reducing or eliminatingthe problem of gas locking.

Another object of the present invention is to provide a subsurface,hydraulically operated pump which employs a hydraulic power fluid and isconstructed so that the power fluid utilized in operating the pump isnot permitted to contact, or mix with, the pumped or produced fluid atany time during the use of the pump.

An additional object of the present invention is to provide a subsurfacehydraulic pump which provides a gas accumulator at the surface whichfunctions to collect gas entrained in the production fluid and tousefully employ such collected gas for directing the produced fluidthrough a discharge line to a storage facility, and also for maintaininga preselected pressure differential across a downhole free workingpiston so that the piston may be operated with maximum efliciency, andlowest power input, using such pneumatic pressure in combination withthe hydrostatic head exerted by the column of production fluid standingin an annulus between a production fluid string and power fluid tubingstring of the pump.

Another object of the invention is to provide a rodless type subsurfacepump which may be manufactured relatively economically and operated withsmall power costs as compared to sucker rod type subsurface pumps, andalso as compared to present hydraulic and pneumatic pumps now in use.

An additional object of the invention is to provide an improvedsubsurface, hydraulically operated rodless pump in which a substantialportion of any sand or other solid contaminant or foreign materialpresent in the fluid produced by the pump is removed prior to the timesuch fluid is moved to the surface by the pump.

An additional object of the present invention is to provide an improvedsubsurface, hydraulic, rodless pump which effectively extracts orremoves a substantial portion of the entrained gas from the productionfluid prior to the time the production fluid reaches the surface.

In addition to the foregoing described objects and advantages,additional objects and advantages will become apparent as the followingdetailed description of the invention is read in conjunction with theaccompanying drawings.

In the drawings:

FIGURE 1 is a schematic, vertical sectional view showing the subsurfacehydraulic pump of the present invention installed in a conventional oilwell casing.

FIGURE 2 is an enlarged sectional view of wellhead apparatus forming aportion of the subsurface pump of the present invention.

FIGURE 3 is a vertical sectional view taken through an upper portion ofthe concentric tubing strings of the subsurface pump of the invention,and through the well casing which surrounds the pump.

FIGURE 4 is a vertical sectional view taken through the concentrictubing strings of the subsurface pump of the invention at a pointimmediately below that portion of the pump illustrated in section inFIGURE 3.

FIGURE 5 is a transverse sectional view taken along line 5-5 of FIGURE4.

FIGURE 6 is a transverse sectional view taken along line 6-6 of FIGURE4.

FIGURE 7 is a transverse sectional view taken along line 77 of FIGURE 4.

FIGURE 8 is a vertical sectional view of the concentric tubing stringsof the subsurface pump of the invention with such sectional view beingtaken through that portion of the pump which is disposed immediatelybelow the portion of the pump depicted in FIGURE 4.

FIGURE 9 is a transverse sectional view taken along line 99 of FIGURE 8.

FIGURE 10 is a transverse sectional view taken along line-10-10 ofFIGURE 8.

FIGURE 11 is a vertical sectional view taken through the concentrictubing strings of the pump at a point in the pump which is immediatelybelow that portion of the pump depicted in FIGURE 8.

FIGURE 12 is a vertical sectional view taken through the lower end ofthe subsurface pump of the present invention.

Referring now to the drawings in detail, and particularly to FIGURE 1,the subsurface pump of the invention is shown extended into a wellcasing 10 which extends downwardly into the earth to an oil bearingformation. An outer or production fluid tubing string of the pump isdesignated by reference numeral 12. At the lower end of the productionfluid tubing string 12 a perforated gas anchor 14 is connected by aspecial connector sub 16 to a sand trap sleeve 18. The sand trap sleeve18 is con nected at its upper end to a seating collar 20. The seatingcollar 20 is connected through subs 21, 22 and 24 to the lower end ofthe production fluid tubing string 12.

Secured to the upper end of the subsurface pump and located above theground thereover is a wellhead assembly designated generally byreference numeral 28. The wellhead assembly includes (as depicted inFIGURES 1 and 2) a production fluid collecting chamber 30 and aproduction fluid discharge conduit 32 in which is interposed a balancedhydrostatic fluid level control valve 34. A power fluid cylinder 36extends downwardly into the collecting chamber 30 and is sealed withrespect thereto by a suitable flange and sealing ring connection 38. Agas pressure gauge 40 is mounted on the top of the production fluidcollection chamber 30 for registering the pressure of a gas 41 occupyingthe upper portion of this chamber.

For the purpose of supplying makeup power fluid to the power fluidcylinder 36, a makeup tank 42 is supported on, or secured to, a suitableflange 44 formed on the collecting chamber 30 and supplies make up powerfluid via a conduit 46 to the upper end of the power fluid cylinder 36.A suitable vented filling cap 48 is provided on the makeup tank 42 forventing gas from the upper portion of this tank in the event anexcessive pressure is built up therein, and also to permit the supply ofmakeup power fluid in the tank to be replenished if necessary. A gasreservoir or accumulator 50 is supported by a suitable bracket 52 on theupper end of the power fluid cylinder 36 and is connected through aconduit 53 to the upper end of the production fluid collection chamber30. A pressure regulator valve 54 is interposed'in the conduit 53 forregulating the pressure differential between the collecting chamber 30and the accumulator 50. In a preferred embodiment of the invention, airmay be supplied to the accumulator 50 by a suitable air compressor 56which is connected to the accumulator 50 through a suitable conduit 58.A pop valve 60 is provided in association with the compressor 56 andaccumulator 50 for relieving excessive pressure in the system.

The aid compressor 56 is driven by a suitable transmission linkage (notvisible) from a motor 62 or other suitable prime mover. The motor 62also functions to drive through a suitable linkage, a crank orconnecting arm 64 which is pivotally connected to the upper end of apiston rod 66 which is coaxially disposed in the power fluid cylinder36. At its end opposite the end connected to the connecting arm 64, thepiston rod 66 carries a fluid piston 68 formed by a series of stacked orsuper-imposed flexible resilient cups. The piston 68 is provided with afirst passageway therethrough in which is interposed a check valve 70.The check valve 70 is constructed to prevent flow of liquid from thelower side of the piston 68 through the piston to the upper sidethereof, but to permit flow of liquid in a downward direction across thepiston and through the check valve. A second passageway is also providedthrough the piston 68, and the entrance to the second passageway isprovided with a pre-set pressure responsive valve 72 which will permitfluid to pass therethrough from the lower side of the piston when thepressure differential across the piston exceeds a preselected value.

Secured through a suitable sub 76 to the lower end of the collectionchamber 30 is the production tubing string designated generally byreference numeral 12. The production tubing string 12 concentricallysurrounds a power fluid tubing string designated generally by referencenumeral 80 which is secured to the lower end of the power fluid cylinder36 and communicates with the interior thereof. The upper sections of thepower fluid tubing string 80 are connected to an upper working barrelportion of the string designated by reference numeral 82 and depicted inFIGURES 3 and 4. The lower end of the production tubing string 12 isconnected to a sub 24 as hereinbefore explained.

Disposed within the working barrel 82 of the power fluid string 80 is acompound power fluid working piston designated generally by referencenumeral 84, and shown in its entirety when FIGURES 3 and 4 areconsidered conjunctively. The compound power fluid working piston is afree piston and includes an upper piston element designated generally byreference numeral 86, a lower piston element designated generally byreference numeral 88, and an elongated connecting rod 90. A fishing neck92 may be conveniently threadedly secured to the upper end of the upperpiston element 86, and this piston element is preferably constructed asa hollow or cylindrical mandrel 94 which carries a plurality of sealingcups 96 which are mounted on the mandrel with a plurality of annularmetallic spacers 98 in a manner well understood in the art. It will benoted that a number of the sealing cups 96 face upwardly and thusfunction to prevent by-pass of the piston by a power fluid acting on thepiston from above, whereas others of the sealing cups face downwardlyand prevent leakage of fluid past the piston from a position therebelow.

The hollow mandrel 94 is connected at its lower end to the elongatedconnecting rod 90, and also threadedly engages an annular guide collar100 which is slightly smaller in outside diameter than the insidediameter of the working barrel 80. The guide collar 100 functions to Lguide the compound working fluid piston 84 during its reciprocatingmovement, but does not absolutely prevent fluid by-pass between theguide collar 100 and the internal wall of the Working barrel 82.

Similarly to the upper piston element 86 of the compound power fluidpiston 84, the lower piston element 88 includes a generally cylindricalmandrel 102 which has mounted thereon a plurality of annular metallicspacers 104 which position and support a plurality of downwardly facingsealing cups 105. The sealing cups 105 bear against the internal wall ofa lower working barrel 106 of the power fluid tubing string 80, andprovide a fluid tight seal therewith. At its upper end, the mandrel 102is internally threaded and receives the lower end of the elongatedconnecting rod 90. It will be noted that the lower end of the elongatedconnecting rod 90 is of reduced diameter and is externally threaded forengagement with the mandrel 102. It will further be noted that the lowerend of the elongated connecting rod 90 is provided with an axiallyextending bore 108 which communicates with the hollow interior of themandrel 102, and which has extending thereinto a plurality of radialports 110 formed through the connecting rod 90. The function of theports 110 and the axial bore 108 will be hereinafter explained.

Adjacent its lower end, the upper working barrel 82 of the power fluidtubing string 80 is connected through a special lubricating sub 112 tothe lower Working barrel 106 of the power fluid tubing string. Thespecial lubricating sub 112 is machined to relatively closely surroundthe elongated connecting rod 90 and is provided with annular grooveswhich accommodate sealing rings 114. The sealing rings 114 provide afluid tight seal between the elongated connecting rod 90 and the speciallubricating sub 112. In its central portion, the special lubricating sub112 has a lubricant chamber 115 which extends around the elongatedconnecting rod 90 and provides a space into which a lubricant may beinjected through a suitable grease or lubricant fitting 116. It will benoted that the grease fitting 116 is located in a recess 118 whichrenders the fitting accessible without requiring its protrusion beyondthe circumference of the working barrels 82 and 106 of the power fluidtubing string 80. The lower end 120 of the special lubricating sub 112is of reduced diameter to permit a decelerating collar 122 which isthreadedly secured to the upper end of the mandrel 102 to be looselyreceived thereover. Stated differently, the decelerating collar 122 hasa large bore formed in the end thereof which is diametrically sized toassure the presence of an annulus between this collar and the reduceddiameter lower end 120 of the special lubricating sub 112. At a pointimmediately above the upper end of the special lubricating sub 112, aplurality of ports or passageways 124 are formed through the upperworking barrel 82 of the power fluid tubing string 80 and it will benoted that an annular bumper member 125 of resilient material looselysurrounds the elongated connecting rod 90 and rests upon the upper endof the lubricating sub 112 at this point.

At its lower end, the cylindrical mandrel 102 is provided with a largethreaded counterbore 126, and an externally threaded pressure reliefvalve assembly designated generally by reference numeral 128 is threadedinto the counterbore 126. The pressure relief valve assembly 128includes a generally cylindrical member 130 having an elongated boreformed in the lower end thereof, and a counterbore 142 communicatingwith the bore 140 at the upper end thereof. A spring 144 is seated inthe counterbore 142 and biases a ball check member 146 against a valveseat 148 which is threaded into the counterbore 142 from the upper endof the pressure relief valve assembly 128.

The lower end of the lower working barrel 106 of the power fluid tubingstring 80 is threadedly connected to a generally cylindrical valve body154. The cylindrical valve body 154 is circumferentially recessed orundercut at its central portion, as indicated by reference numeral 156,for the accommodation of a pivoted valve assembly designated generallyby reference numeral 158. The construction of the pivoted valve assembly158 can be best understood by reference to FIGURES 8 and 9, and includesa supporting ring 160 which surrounds the recessed portion 156 of thecylindrical valve body 154 and carries a plurality of cars (not seen)which pivotally support three valve arms 162. The valve arms 162 arethus each free to pivot about a horizontal axis. Adjacent their upperends, each of the valve arms carries a recess 164 which accommodates asmall ball valve 166. The ball valves 166 seat in and close radial ports170 provided around the periphery of the cylindrical valve body 154 inthe recessed portion 156 thereof. The pivoted valve arms 162 areretained in their seated positions as depicted in FIGURES 8 and 9 by acircumferential or annular coil spring 172 which extends around all ofthe valve arms and biases them inwardly. From the described constructionof the pivoted valve assembly 158, it will now be understood that theassembly functions to provide a plurality of check valves acting toclose the ports 170 against the flow of fluid from the annulus betweenthe production fluid tubing string 12 and the power fluid tubing string80.

The lower end of the cylindrical valve body 154 is provided with alarge, threaded counterbore 176 into which is threaded a valve cage 178.The lower end of the cylindrical valve body 154 is also externallythreaded for threaded engagement with a tapered seating nipple 180. Thevalve cage 178 is an elongated, generally cylindrical member having aball limiting restriction 182 formed at the upper end thereof, andhaving a plurality of elongated ports 184 formed below the restriction182 to permit production fluid to pass from the inside of the valve cage178 into the counterbore 176 formed in the lower end of the cylindricalvalve body 154. The lower end of the valve cage 178 is provided with adownwardly facing shoulder 186 and a valve seat 188 abuts against theshoulder and supports a spherical or ball-shaped standing valve 190. Thevalve seat 188 is retained against the shoulder 186 by a retaining tube192.

The retaining tube 192 is pressed through a seating nipple plug 194, andthis plug is threaded into the lower end of the seating nipple 180. Theseating nipple plug 194 is peripherally grooved for the accommodation ofan O-ring seal 196. The O-ring seal 196 sealingly engages the internalwall of a seating collar 198 which is provided with a tapering bore atits upper end for receiving and seating the seating nipple 180. Theseating collar 198, which is connected at its upper end to the sub 21,is a generally cylindrical member having a plurality of axiallyextending, circumferentially spaced passageways 200 formed through thewall thereof as best illustrated in FIGURES 8 and 9. The passageways 200communicate with the annulus which is defined between the cylindricalvalve body 154 and the sub 21 interposed in the production tubing string12. The passageways 200* also communicate at their lower ends with anannulus 204 formed between an elongated sand trap sleeve 206 and aproduction fluid pipe 208. The production fluid pipe 208 is threaded atits upper end into a connector fitting 210- by which it is threadedlyconnected to the inside of the lower end portion of the seating collar198. The sand trap sleeve 206 is externally threaded and is threadedlyengaged with threads formed in a large counterbore 212 positioned at thelowermost end of the seating collar 198.

The production fluid pipe 208, as shown in FIGURE 12, extends through apacking 211 which is retained against a shoulder 213 in a specialconnector sub 214 by a threaded retaining ring 216. The specialconnector sub 214 has a large, internally threaded counterbore at itsupper end which threadedly receives the lower end of the sand trapsleeve 206. The special connector sub 214 also has a large, internallythreaded counterbore at its lower end which threadedly receives theupper end of a perforated, generally cylindrical gas anchor 218.

Intermediate its length, the gas anchor 218 is provided 1 with aplurality of perforations or apertures 220. The gas anchor surrounds aproduction fluid pick up tubing 222 which is threadedly connected at itsupper end through a connecting sleeve 224 to the lower end of theproduction fluid pipe 208.

Operation In the operation of the subsurface pump of the invention, thepower fluid tubing string 80 is initially filled with power fluid sothat the space in this tubing string between the compound working piston84 and the power fluid piston 68 located at the top of the well in thepower fluid cylinder 36 is completely filled with a power fluid. Thepower fluid is preferably a relatively inert, low volatilitynon-corrosive vegetable oil. A special heat resisting oil which containsand develops practically no gas at high bottom hole temperatures ispreferably employed. At the time of filling the power fluid tubingstring 80 in the space between the working piston assembly 84 and thepower fluid piston 68, it is preferred that both the power fluid pistonand the working piston assembly 84 be in their lowermost positions. Thisarrangement assures that the length of the column of power fluid betweenthese two elements of the subsurface pump will correspond to thevolumetric displacement which will be required to characterize the powerfluid column during all portions of the pump stroke. An additionalamount of the power fluid is placed in the power fluid cylinder 36 abovethe power fluid piston 68, and the power fluid makup tank 42 is filledwith makeup power fluid and is connected to the power fluid cylinder 36through the conduit 46. In some instances, in order to provide for themost expeditious full stroke, complete cycle operation of the subsurfacepump, it may be desirable to fill the production fluid collectionchamber 30 and the production fluid tubing string .12 with oil or othersuitable, low cost fluid at the outset of the pumping operation to primeor assist the initial stroking of the pump as hereinafter described.This expedient is not a requirement, however, in the operation of thepump.

Prior to starting the operation of the motor of prime mover 62, theaccumulator or reservoir of compressed gas is connected through theconduit 53 to the upper portion of the collection chamber 30, but it ispreferred that no gas is passed into the upper portion of the collectionchamber. As the motor 62 is started up, the piston rod 66 drives thepower fluid piston 68 in reciprocation. As a result of this motion ofthe power fluid piston 68, the column of power fluid which is positionedbetween this piston and the compound working piston 84 is alsoreciprocated and drives the compound working piston 84 in reciprocation.During the upstroke of the power fluid piston 68, the vacuum created bythis upstroke, coupled with the hydrostatic force exerted by the columnof production fluid standing in the annulus between the production fluidtubing string 12 and the power fluid tubing string will simultaneouslypull and push the compound working piston 84 upwardly in the power fluidtubing string 80. It will be noted that the production fluid collectionchamber 30 is of relatively large diameter as compared to the diameterof the production fluid tubing string 12 and the power fluid tubingstring 80, so that a relatively large movement of the compound workingpiston 84 in the power fluid tubing string will not result in a largesubsidence in the level of the production fluid contained within theproduction fluid collection chamber 30 as production fluid follows thecompound working piston 84 upwardly in the power fluid tubing string.

It is to be noted that the working area of the power fluid piston 68 ismany times greater than the crosssectional area of the upper pistonelement 86 of the compound working piston 84. Thus, a relatively shortstroke of the power fluid piston 68 is multiplied to produce a longstroke by the working piston 84.

On the upstroke of the compound working piston 84, oil, water or otherfluid to be produced by the subsurface pump is drawn inwardly throughthe perforations or apertures 220 in the gas anchor 218 located at thelower end of the subsurface pump. This gas anchor is, of course,disposed opposite the fluid producing formation so that the productionfluid can flow freely through the perforations 220. In the case of oilwhich has a high gas content, as such oil is drawn through theperforations 220 in the gas anchor 218, a substantial portion of any gaswhich is entrained therein tends to weather off, or to move upwa-rdlyinto the upper portion of the gas anchor 218 and is there entrapped. Theliquid hydrocarbon, on the other hand, moves downwardly in the annulusbetween the production fluid pickup tubing 222 and the gas anchor 220.

In the lower end of the gas anchor 218, the production fluid turnsupwardly in the subsurface ump and enters the open lower end of theproduction fluid pickup tubing 222. Continued upward movement of thecompound working piston 84 draws the production fluid through theconnecting sleeve 224 and into the production fluid pipe 208. The

production fluid pipe 208 conveys the production fluid into the interiorof the seating collar 198 and, from this point, the production fluidmoves upwardly through the retaining tube 192, past the standing valve190, which is opened during the upstroke of the pump, and through theelongated ports 184 in the upper end of the valve cage 178. Since theupstroke of the compound working piston 84 coupled with the action ofspring 172 draws the valve elements of the pivoted valve assembly 158 totheir closed position where they are held on their seat by thehydrostatic pressure in the production string, the production fluidcontinues upwardly and enters the lower working barrel 106 of the powerfluid tubing string 12. At the top of the stroke of the power fluidpiston 68, the lower piston element 88 of the compound working piston 84occupies the position depicted in FIGURE 4 in which the deceleratingcollar 122 loosely surrounds the lower end 120 of the speciallubricating sub 112. The importance of this relationship of theseelements which occurs at the upper end of the stroke will be hereinafterdescribed in greater detail.

During the downstroke of the pump, the compound working piston 84 isdriven downwardly in the upper Working barrel 82 of the power fluidtubing string 12 by the impress of the power fluid directed downwardlyin the power fluid tubing string by the downward reciprocation of thepower fluid piston 68. The length of the column of power fluid betweenthe power fluid piston 68 and the compound working piston 84 is suchthat the lower limit of the stroke will occur at a time when the lowerpiston element 88 of the compound working piston 84 is adjacent thegenerally cylindrical valve body 154. At this time, the generallycylindrical member 130 will project downwardly into the bore through thegenerally cylindrical valve body 154 so as to provide a loose fittherewith and to result in a dash pot or decelerating effect ashereinafter described.

During the downstroke of the compound working piston 84, productionfluid standing in the lower working barrel 106 below the lower pistonelement 88 is forced downwardly by the lower piston element. This actionresults in seating the ball-shaped standing valve 190, and opening ofthe ball valves 166 forming a part of the pivoted valve assembly 158.This opens the ports 170 and permits the production fluid to movethrough these ports into the annulus between the production tubingstring 12 and the power fluid tubing string 80. As production fluidmoves through the ports 170 into the annulus, a tendency exists to throwout of the production fluid by centrifugal force, a substantial amountof any sand which may be entrained in the production fluid, such sandsettling into the annulus between the lower end of the cylindrical valvebody 154 and the surrounding sub 21. This gravitating sand then moves ondownwardly through quiescent production fluid which stands in thisspace, through the axially extending passageways 200 formed in theseating collar 198 and into the sand trap sleeve 206. The sand thusultimately accumulates at the bottom of the sand trap sleeve 206 and ontop of the closure which is formed or constituted by the specialconnector sub 214. It may be noted at this point that after extendedperiods of operation of the subsurface pump, the sand trap sleeve 206may become substantially filled with sand, and it will be desirable topull the pump and clean the sand trap sleeve 206 to remove all theaccumulated sand therefrom. This may be easily accomplished by simplydisconnecting the sand trap sleeve 206 from the special connector sub214, and from the lower end of the seating collar 198.

Continued downward movement of the compound working piston 84 continuesto drive the production fluid accumuated in the lower working barrel outthrough the ports 170 and up into the annulus between the productionfluid tubing string 12 and the power fluid tubing string 78. This willresult in an increase or elevation of the level of production fluidstanding in the production fluid collection chamber 30 at the surface.Any residual 10 gas entrained in the production fluid will be ventedinto the upper portion of the collection chamber 30. The balancedhydrostatic fluid level control valve 34 which is interposed in theproduction fluid discharge line 32 can be preset to respond periodicallyto the hydrostatic and pneumatic pressures ac.ing from inside theproduction fluid collection chamber 30 so that the valve 34 opens andcloses periodically to automatically retain the level of the productionfluid in the colle.-tion chamber 30 between certain predeterminedlimits. The purpose of this arrangement is to provide maximum assistanceto the pumping action of the power fluid piston 68 as a result of thepresence in the annulus between the tubing strings of a standing columnof production fluid, and the presence in the upper portion of theproduction fluid collection chamber 30 of a gas under pressure. Thus, bycontinuously maintaining the production fluid in the collection chamber30 at a substantial depth, and retaining gas pressure in the upperportion of this chamber at a certain preselected value, hydrostatic andpneumatic forces may be brought to bear to assist the power fluid piston68 during its upstroke in the retraction or upward movement of thecompound working piston 84.

The precise manner in which the hydrostatic force exerted by the columnof production fluid standing in the annulus between the tubing stringsis brought to bear may be better understood by reference to FIGURE 4 ofthe drawings. In referring to this figure, it will be noted that theports or passageways 124 remain open constantly and thus permitcontinuous communication be.ween the interior of the working barrel 82and the annulus between this working barrel and the production fluidtubing string 12. The production fluid retained in this annulus istherefore, at all times, in communication with the interior of theworking barrel 82, and fills the space above the special lubricating sub112 and the lower side of the upper piston element 86 of the compoundWorking piston 84. Thus, the hydrostatic force developed by the columnof production fluid in the annulus between the tubing strings exerts aconstantly ac.ing, upwardly directed force against the lower side of theupper piston element 86, and tends toforce the compound working pistonassembly 84 upwardly during the upstroke of the pump. This upward forceis further augmented by the downwardly acting pressure of gas retainedunder compression in the upper portion of the collection chamber 30. Thecombined hydrostatic and pneumatic forces can be adjusted so that verylittle power must be applied by the prime mover 62 through the pistonrod 66 to the power fluid piston 68 in order to retract this piston inan upward direction, and to have the piston followed by the column ofpower fluid which is positioned between the power fluid piston and theupper piston element 86 of the compound working piston 84.

A more selective and "versatile control of the pneumatic assistanceprovided to the pumping action is attained in the illustrated preferredembodiment of the invention by the inclusion in the system of thepressure gauge 40 and the gas reservoir or accumulator 50 and associatedcontrols. By means of these elements, air or other gas under pressuremay be introduced to the upper end of the production fluid collectionchamber 30 at a desired pressure so as to retain the gas pressure inthis chamber at a desired value. The compressor 56 may be operated fromthe prime mover 62 to constantly regenerate pressure in the accumulator50 so that a constant supply of gas under pressure is available in theeventthe system should develop leaks, or the pumping of a relativelyhigh viscosity material should require a higher pressure in thecollection chamber 30.

An important feature of the present invention is the characteristic ofthe subsurface pump of maintaining a relatively constant volume of powerfluid between the power fluid piston 68 and the compound working piston84. In many rodless pumps of general similarity to the present inventionin which a column of power fluid has been provided to extend between areciprocating piston located at the surface and a working piston locatedwithin a power fluid string in the well, some difficulty has beenexperienced in maintaining a constant volume characteristic of thiscolumn of power fluid. This difficulty has been in part due to leakageor loss of power fluid from this zone through evaporation and the like.When such loss occurs, the length of stroke of the working piston may beshortened, or the working piston may be made to move through a pathwhich is substantially less than optimum. As contrasted with such powerfluid losses, a disruption in smooth and eflicient pumping operationsmay occur in the rodless pumps of the prior art as a result of the powerfluid between the power fluid piston and the working piston becoming hotand expanding so as to occupy a greater volume. When this occurs, theeffect is to cause the freely mounted working piston to be displacedfurther down into the power fluid tubing string with the result that itsfull stroke may bring it into contact with stops or other elements in aforcible manner so as to damage the pump.

In order to accommodate or make provision for the described loss ofpower fluid, or the expansion of the body of power fluid between thepower fluid piston and the working piston, the present inventionincorporates a novel arrangement for adding makeup power fluid to thiscolumn of power fluid when losses occur, or for bypassing and removingpower fluid where the volume of power fluid is undesirably increased asresult of thermal expansion. The structure for accomplishing thesefunctions is best illustrated in FIGURE 2 of the drawings. It will therebe noted that a downwardly opening check valve 70 is provided in apassageway which extends through the power fluid piston 68, and that asecond passageway extended through this piston is provided with a presetpressure responsive valve 72. Where fluid is lost from the column ofpower fluid between the power fluid piston 68 and the compound workingpiston 84, the result is the creation of a pressure differential acrossthe power fluid piston 68 during the upstroke which causes power fluidabove this piston to move through the open check valve 70 and to fillthe void resulting from loss of power fluid below the piston. In otherwords, when power fluid is lost from the column, a partial vacuum iscreated on the lower side of the power fluid piston 68.

during its upstroke, and this partial vacuum causes the check valve 70to open, and draws power fluid standing in the power fluid cylinder 36above the power fluid piston 68 downwardly through the passageway. Thismakeup power fluid is added to the column of power fluid below thepiston 68. Thus, the constant volume of power fluid required in thisspace is maintained despite small losses of such fluid over a period ofextended operation.

In those instances where the power fluid between the power fluid piston68 and the compound working piston 84 has been expanded due to heating,such expansion will tend to increase the volume of power fluid in thecolumn, and the result will be that on the downstroke of the power fluidpiston 68, the lower end of the upper piston element 86 will be drivenagainst the bumper 125 positioned on the upper end of the speciallubricating sub 112. Once the downward movement of the compound workingpiston 84 is positively arrested in this manner, continued downwardmovement of the power fluid piston 68 will result in a tendency tocompress the power fluid column standing in the power fluid tubingstring 80. Such compression overcomes the clgsing bias of the pressureresponsive valve 72, and permits the excessive power fluid disposed inthe column to be vented or bled through the passageway in the powerfluid piston 68 in which the pressure responsive valve 72 is located.Then on the next upstroke of the pump, the precise and desired amount ofpower fluid will be located between the compound working piston 84 andthe power fluid piston 68. In order to assure that a readily availablesupply of makeup power fluid is constantly available above the powerfluid piston 68, the makeup power fluid tank 42 is provided, and feedsmakeup power fluid through the conduit 46 to the upper end of the powerfluid cylinder 36.

The subsurface pump of the invention is smooth in its operation andlittle or no chattering or bumping occurs. Smoothness of operation isachieved by the provision of dash pot effects at each end of the strokeof the compound working piston 84. Thus, during the upstroke of thecompound working piston 84, the decelerating collar 122 moves upwardlyto a position at the end of the stroke in which it surrounds the reduceddiameter lower end of the special lubricating sub 112. As these elementsmove into this relationship, any fluid which may be entrappedtherebetween, whether it be gas, or production fluid which has bypassedthe sealing cups 105, is entrapped in the restricted annular zonebetween the reduced diameter lower end 120 of the special lubricatingsub 112 and the decelerating collar 122. This fluid will be passedthrough the small radial ports 110 and into the axial bore 108 formed inthe lower end of the connecting rod 90. The fluid displaced through theradial ports 110 at the end of the upstroke of the compound workingpiston 84 will move into the hollow interior of the cylindrical mandrel102 and will there accumulate until such time as the pressure of thefluid in this zone becomes great enough to open the ball check member146 against the bias of its spring 144 and permit venting of theinterior of the mandrel 102. The fluid accumulated within the mandrel102 is, of course, vented through the ball check member 146 into theopen interior of the lower working barrel 106 below the lower pistonelement 88.

On the downstroke of the pump, the dash pot decelerating effect isobtained by the entry of the lower end of the generally cylindricalmember into the interior of the generally cylindrical valve body 154.

From the foregoing description of the invention, it will be perceivedthat the subsurface pump described provides ahydraulichydrostatic-pneumatic pump actuation which results in a lowexternal power requirement for the pump, and which, because of the useof a simple power piston at the surface, involves a low initialinstallation cost. A substantial portion of any entrained gas or sand isremoved during the operation of the pump so that the produced fluid isrelatively clean, and requires a minimum of processing prior topipelining or ultimate use. No mixing of the power fluid with theproduction fluid occurs during the operation of the pump, and theprovision of structure for maintaining a constant volume of power fluidin the power fluid column extending between the working piston in thewell and the power fluid piston at the surface assures an extended andtrouble-free operating life. The pumping stroke pressure of the downholepump is in a downward direction, and therefore no unseating of the pumpbarrel occurs. Additional hydrostatic and pneumatic pressure constantlyact downwardly in the pump through the annulus of the production string.These downwardly acting forces all prevent pumping off or lifting of thedownhole pump from its seating nipple, a common, undesirable occurrencein many types of downhole pumps heretofore in use.

Although certain preferred embodiments of the present in vention havebeen hereinbefore described and depicted in the accompanying drawings,it will be understood that various modifications and changes may beeffected in the illustrated structure without departure from the basicprinciples. which underlie the invention. Insofar as such changes andmodifications do not entail a departure from the basic principles of theinvention, such changes and modifications are deemed to be circumscribedby the appended claims or reasonable equivalents thereof.

What is claimed is:

1. A subsurface pump comprising:

a power fluid tubing string;

a production fluid tubing string concentrically surrounding the powerfluid tubing string and defining an annulus therewith;

a power fluid cylinder connected to the upper end of said power fluidtubing string;

a power fluid piston reciprocably disposed in said power fluid cylinder,said power fluid piston having a pair of power fluid passagewaysextending therethrough;

valve means in said power fluid passageways for selectively passingpower fluid across said power fluid piston whereby a substantiallyconstant volume of power fluid may be maintained below said power fluidpiston;

prime mover means drivingly connected to said power fluid piston fordriving said power fluid piston in reciprocation in said power fluidcylinder;

a free, working piston reciprocally and slidingly dis- A posed in saidpower fluid tubing string, said free, working piston including an upperpiston element and a lower piston element and an elongated connectingrod interconnecting the upper and lower piston elements;

first check valve means disposed in the power fluid tubing String belowthe free piston for permitting flow of production fluid upwardly in thepower fluid tubing string while preventing the flow of fluid downwardlypast the check valve;

first passageway means extending through the power fluid tubing stringat a location between said first check valve means and the free, workingpiston and placing the annulus between the tubing strings incommunication with the interior of the power fluid tubing string;

second check valve means disposed in said first passageway means forpreventing the flow of production fluid from said annulus into saidpower fluid tubing string through said first passageway means;

second passageway means extending through the power fluid tubing stringat a location which is always disposed between said upper and lowerpiston elements during reciprocation of said free, working piston, saidsecond passageway means placing the interior of said power fluid tubingstring in communication with the annulus between said tubing strings;

a tank for making power fluid positioned adjacent said power fluidcylinder;

a conduit connected between said tank and power fluid cylinder forintroducing'makeup power fluid from said tank to said cylinder on theopposite side of said power fluid piston from its side nearest adjacentsaid power fluid tubing string;

upper end of said production fluid tubing string for receivi gproduction fluid therefrom;

means for periodically discharging production fluid from said collectionchamber to maintain the level of production fluid in said collectionchamber within predetermined limits;

an air compressor drivingly connected to said prime mover; and

conduit means connected between said air compressor and said collectionchamber for introducing air under pressure to said collection chamber.

2. A subsurface pump comprising:

a power fluid tubing string;

a production fluid tubing string concentrically surroundthe power fluidtubing string and defining an annulus therewith;

means for periodically delivering power fluid under pressure to saidpower fluid tubing string;

a free, working piston reciprocally and slidingly disposed in said powerfluid tubing string, said free,

production fluid collection chamber connected to the r working pistonincluding an upper piston element and a lower piston element and anelongated connecting rod interconnecting the upper and lower pistonelements;

first check valve means disposed in the power fluid tubing string belowthe free piston for permitting flow of production fluid upwardly in thepower fluid tubing string while preventing the flow of fluid downwardlypast said first check valve means;

first passageway means extending through the power fluid tubing stringat a location between said first check valve means and the free pistonand placing the annulus between the tubing strings in communication withthe interior of the power fluid tubing string;

a generally cylindrical valve body connected in the lower end of thepower fluid tubing string and having said first passageway meansextending radially therethrough;

at least one valve arm pivotally mounted on the outside of saidcylindrical valve body for pivotation about a horizontal axis;

a valve closure member carried by each of said valve arms and positionedthereon for closing said first passageway means in one position of therespective pivotally mounted valve arms;

annular spring means surrounding said generally cylindrical valve bodyand said valve arms, and biasing said valve arms to a position in whichsaid valve closure members bear against said cylindrical valve body andclose said first passageway means;

second passageway means extending through the power fluid tubing stringat a location which is always disposed between said upper and lowerpiston elements during reciprocation of said free, working piston, saidsecond passageway means placing the interior of said power fluid tubingstring in communication with the annulus between said tubing strings;and

power fluid makeup means connected to said means for periodicallydelivering said power fluid for supplying makeup power fluid thereto.

3. A subsurface pump comprising:

a power fluid tubing string;

a production fluid tubing string concentrically surrounding the powerfluid tubing string and defining an annulus therewith;

a power fluid cylinder connected to the upper end of said power fluidtubing string;

a power fluid piston reciprocably disposed in said power fluid cylinder,said piston having first and second power fluid passagewaystherethrough;

a preset pressure responsive valve connected to said first power fluidpassageway through said power fluid piston for selectively controllingthe passage of a power fluid from said power fluid tubing string to theopposite side of said power fluid piston from said power fluid tubingstring;

a check valve in said second passageway through said power fluid pistonfor permitting flow of power fluid from above said power fluid pistonthrough said power fluid piston toward said power fluid tubing string,and preventing power fluid flow in the opposite direction through saidsecond passageway;

prime mover means drivingly connected to said power fluid piston fordriving said power fluid piston in reciprocation in said power fluidcylinder;

a tank for makeup power fluid positioned adjacent said power fluidcylinder;

a conduit connected between said tank and said power fluid cylinder forintroducing makeup power fluid from said tank to said power fluidcylinder on the opposite side of said power fluid piston from said powerfluid tubing string;

a free, working piston reciprocably and slidingly disposed in said powerfluid tubing string, said free,

working piston including an upper piston element, and a lower pistonelement, and an elongated connecting rod interconnecting the upper andlower piston elements;

a column of power fluid of constant volume disposed between said free,working piston and said power fluid piston;

means secured in said power fluid tubing string and slidingly andsealingly surrounding said elongated connecting rod at a locationbetween said upper and lower piston elements;

first check valve means disposed in the power fluid tubing string belowthe free, working piston for permitting flow of production fluidupwardly in the power fluid tubing string While preventing the flow offluid downwardly past the check valve means;

first passageway means extending through the power fluid tubing stringat a location between said first check valve means and the free pistonand placing the annulus between the tubing strings in communication withthe interior of the power fluid tubing string;

second check valve means disposed in said first passageway means forpreventing the flow of production fluid from said annulus into saidpower fluid tubing string through said first passageway means; and

second passageway means extending through the power fluid tubing stringat a location which is always disposed between said upper and lowerpiston elements and above said means slidingly and sealingly surroundingsaid elongated connecting rod during reciprocation of said free, workingpiston, said second passageway means placing the interior of said powerfluid tubing string in communication with the annulus between saidtubing strings.

4. A subsurface pump as defined in claim 3 and further characterized toinclude a production fluid collection chamber connected to the upper endof said production fluid tubing string for receiving production fluidtherefrom; and

means for periodically discharging production fluid from said collectionchamber to maintain the level of production fluid in said collectionchamber within predetermined limits.

5. A subsurface pump comprising:

a power fluid tubing string;

a production fluid tubing string concentrically surrounding the powerfluid string and defining an annulus therewith;

means for periodically delivering power fluid under pressure to saidpower fluid tubing string;

a free, working piston reciprocally and slidingly disposed in said powerfluid tubing string, said free, working piston including an upper pistonelement and a lower piston element and an elongated connecting rodinterconnecting the upper and lower piston elements;

first check valve means disposed in the power fluid tubing string belowthe free piston for permitting flow of production fluid upwardly in thepower fluid tubing string while preventing the flow of fluid downwardlypast the first check valve means; I

first passageway means extending through the power fluid tubing stringat a location between said first check valve means and the free pistonand placing the annulus between the tubing string in communication withthe interior of the power fluid tubing string; second check valve meansdisposed in" said first passageway means for preventing the flow ofproduction fluid from said annulus into said power fluid tubing stringthrough said first passageway means;

second passageway means extending through the power fluid tubing stringat a location which is always disposed between said upper and lowerpiston elements during reciprocation of said free, working piston, saidsecond passageway means placing the interior of said power fluid tubingstring in communication with the annulus between said tubing string;

power fluid makeup means connected to said means for periodicallydelivering power fluid for supplying makeup power fluid thereto;

a production fluid collection chamber connected to the upper end of saidproduction fluid tubing string for receiving production fluid therefrom;

means for periodically discharging production fluid from said collectionchamber to maintain the level of production fluid in said collectionchamber within predetermined limits;

a prime mover connected to said means for periodically delivering powerfluid under pressure to said power fluid tubing string;

an air compressor drivingly connected to said prime mover; and

conduit means connected between said air compressor and said collectionchamber for introducing air under pressure to said collection chamber.

6. A subsurface pump defined in claim 3 and further characterized toinclude:

a seating collar connected in said production fluid string below saidfirst passageway means and having a downwardly extending passagewaytherethrough communicating at its upper end with the annulus betweensaid production fluid tubing string and said power fluid string forreceiving sand gravitating downwardly in said annulus from the level ofsaid first passageway means;

a tubular sand trap sleeve connected to the lower end of said seatingcollar and having its hollow interior in communication with thepassageway through said seating collar for receiving sand therefrom; and

means closing the lower end of the sand trap sleeve.

References Cited UNITED STATES PATENTS 1,643,616 9/1927 Zinn et al. 10344 1,922,264 8/1933 Shimer 103--46 2,277,306 3/1942 Coffey 103 442,386,564 10/1945 Mumk 103-203 3,304,870 2/1967 Growell et al. 103-44FOREIGN PATENTS 673,850 1/1930 France.

ROBERT M. WALKER, Primary Examiner.

U.S. Cl. X.R. 10346, 220

